1987 mercruiser 165hp 3.7

[krepe]

I am at a loss.. I bought this boat 2 months ago, this is my first boat, im learning as i go. When i bought the boat the guy that i bought it from had the exhaust manifold machined because it had a small leak, impeller and water pump changed, new plugs/wires. i took the boat out and i over heated. i was at no wake speed for about 15 minutes, i gave some throttle because i was out in the open and within a few minutes i overheated, lots of steam everywhere, i immediately shut it down for a good 30 minutes, refilled the water and idled back in. my temp guage doesn't work so i dont know any temps unfortunately. i had a mechanic come by and he changed the impeller and water pump because he said it was tightened too much and it wasnt working properly, he also changed my gimbal bearing and a seal in the drive because the drive fluid was leaking out, the boat ran like complete crap and said i had either ignition or carb issues(i had no idea the boat was running badly,this is my first boat). the mechanic rubbed me the wrong way so i brought it to another mechanic. this mechanic said the previous owner had the wrong plugs in it and put the right ones in. he also cleaned and rebuilt the carb, my boat ran awesome after that! except one thing, i still over heat! i am over a grand in parts and labor at this point so i called everywhere for help/advice and they are all saying my riser is bad/clogged or i have a clogged hose somewhere. the new mechanic said he did notice that the amount of water being pumped out of the motor while connected to a hose wasnt as much as he thought it should be. since 3 people said i have a clogged riser i decided to take it off and take a peek, it is rusted and built up a little on the inside but nothing is clogged by any means so i put it back on. i also tested the t/stat and it works fine under boiling water. i was told to back flush the hose going to the outdrive which i did and it just builds up pressure and just kinda drips out of the outdrive from the back somewhere. i just read that there is a valve in them and wont let water out only in so im assuming thats why i couldnt backflush through that hose? please somebody help me, im at the point where im going to put a for sale sign on it.. i really want to enjoy my boat with my family.
thanks ahead of time for your time, phill

www.pearlcellular.com

 

[dubs283]

Re: 1987 mercruiser 165hp 3.7

i just read that there is a valve in them and wont let water out only in

where did you read this?? (it is wrong)

there is no valve in the sea water supply line

if you aren't getting water to flush out the drive you have a blockage somewhere, weeds/debris/impeller pieces/kinked water passege hose/etc...

 

[krepe]

Re: 1987 mercruiser 165hp 3.7

thats actually great to hear, that means theres some hope. how do i unblock this hose? what is the best/easiest way? it goes through the transom and then down through the drive which i cannot get at.
thanks!

 

[dubs283]

Re: 1987 mercruiser 165hp 3.7

it goes through the transom and then down through the drive which i cannot get at.

why can't you get to it at the transom assy??

its right there port side, just turn the drive to the stbd side and you will see the passage hose

pull the drive and check the passages

 

[krepe]

Re: 1987 mercruiser 165hp 3.7

i just read this on another mercruiser motor. i know it is a different year and model just thought there was a possibility it could be the same on mine.


"I just looked at your cooling system routing for a 2008 Mercruiser 350 mag MPI engine and noticed that you may have a plastic water check valve that is inline on the hose"

 

[krepe]

Re: 1987 mercruiser 165hp 3.7

i have to pull the whole drive off to do this or can i somehow unhook that hose without taking the drive off?
thanks

 

[dubs283]

Re: 1987 mercruiser 165hp 3.7

you can see the hose with out pulling the drive but if you need to replace it, you will have to pull the drive and the bellhousing

to inspect the drive water passages you will have to pull the drive

 

[stonyloam]

Re: 1987 mercruiser 165hp 3.7

OK most of the people advising you have no clue. It is not a clogged riser because you have a closed cooling system with antifreeze that circulates through the exhaust manifold. On a seawater cooled system the riser can become clogged and block the water flow, on your engine the seawater used to cool the heat exchanger (long black tube) is simply dumped into the exhaust behind the riser. I would suggest that your heat exchanger probably needs cleaning, or you have some other blocage in the seawater half of the cooling system. Download manual #8 for the MCM 3.7, 470 engine ( I don't have the link, but I am sure someone here can give it to you) and follow the instructions. You probably should do a compression check to make sure the head gasket is OK. Stick with us, we'll get you on the water. Welcome to the 470 club

 

[krepe]

Re: 1987 mercruiser 165hp 3.7

thankyou so much. i didnt say in any of my posts but i did clean the heat exchanger with wire in every little hole, there was a piece of impeller clogging one of them and compression check was done and all came out good. when we replaced the impellar and water pump the first time, there was impeller everywhere including the heat exchanger. the previous owner didnt remove any of the broken pieces everywhere, just replaced the pump and impeller, all were removed. only thing that hasnt been checked mentioned in previous post was the water inlet hose, i tried backwashing with a hose and no luck, hose just builds pressure and water wont go thru just drizzles out the drive on bottom. im assuming its very plugged?
thanks, phill

 

[dccordell]

Re: 1987 mercruiser 165hp 3.7

I found parts of my impeller in the hose on the back of the transom... I had to push them out from the inside of the boat with a thick wire because they were jammed in there good. That could be your problem, especially since you said you found pieces in the rest of the cooling system too.

The drive does have to come off the boat to check that hose.. Unless you can run a wire down into the hose from the inside and feel around for obstructions. I would pull it off, it's not hard. You might even get away with using the old (recently replaced?) gaskets.

The manual is a must!

 

[krepe]

Re: 1987 mercruiser 165hp 3.7

when i put the hose on that water inlet hose should water have just freely went through and pour out the drive? or should pressure have built up like it did and just drizzle out of the drive? if you say it should have freely went through and pressure not build up then this is the problem. when the pressure built up i had to stop spraying the hose because i would have gotten soaked, it wolluld barely go through.
thanks, phill

 

[krepe]

Re: 1987 mercruiser 165hp 3.7

yeah, the drive was recently off so im assuming he put new gaskets on there. i didnt see him put the drive back on but im sure if they needed to be replaced he would have replaced them. im gonna try and download that manual right now and take a look at it before calling it a night. i cant sleep all i think about is fixing this boat. im banging my head on the wall.
thanks for your help.

 

[dccordell]

Re: 1987 mercruiser 165hp 3.7

Where exactly are you hooking your hose to try to back flush? Are you talking about the hose inside the boat that goes to the transom? I would think that hose would flow water out of the drive pretty fast if it's clear..

 

[krepe]

Re: 1987 mercruiser 165hp 3.7

yes. this hose comes through the transom and it is a few feet long because it runs up the side of the motor to the front of the heat exchange. i was unhooking it from the heat exchange and putting the hose on it. yeah i could barely get water through it.

 

[dccordell]

Re: 1987 mercruiser 165hp 3.7

Ah ok you must not have the factory voltage regulator any more if that hose runs straight to the heat xchanger, which is pretty normal so no worries..

Yeah check out that hose and see why water won't go through... If water can't go through, well.. You know what it does!!

 

[krepe]

Re: 1987 mercruiser 165hp 3.7

on the transom, the hose connects to a plastic piece which has a square housing. is the voltage regulator there? im looking at the manual and its showing the voltage regulator there and the other end is connected to the heat exchange in the maual also.
thanks.

 

[dccordell]

Re: 1987 mercruiser 165hp 3.7

Well that sure does sound like the voltage reg, especially if the manual says so! I guess that is one of the differences between the 165hp model and the others... I didn't know they ever put the voltage regulator on the transom like that, but ok! It sounds like where you are hooking your water hose is trying to force water back through the voltage regulator, too, before going thru the transom, right? The voltage reg could have some pieces lodged in it too... you might could check that first before you take the outdrive off. Although, it would still be a good idea to take it off to see if any more pieces come out the back... if the pieces are indeed stuck in the hose or regulator, during a back flush, where are they going to come out at? I don't think they would make it past the impellar, and then when you crank the motor the impellar might get tore up cuz it's got pieces laying all around in it. I don't know for sure on that, but it's a thought..

That should give you some places to start looking...

 

[dn010]

Re: 1987 mercruiser 165hp 3.7

Why not just replace the hoses and be done with it?? It is simple to replace the one running from the nipple in the transom to the V/R and then from the V/R on... Take the plastic screen off your drive and see if there is any crud in there. If it was me-for piece of mind, I'd pull at least the lower drive and make sure there is nothing in the passages as well AND double check the impeller. As I suggested, I'd also replace ALL hoses (not just for clogs but for age too!) - I really don't want to worry about these things when I'm 5-10 miles off the coast...

 

[04fxdwgi]

Re: 1987 mercruiser 165hp 3.7

yes. this hose comes through the transom and it is a few feet long because it runs up the side of the motor to the front of the heat exchange. i was unhooking it from the heat exchange and putting the hose on it. yeah i could barely get water through it.

If I read this correctly, you are trying to backflush the raw water system thru the hose that connects the transom to the heat exchanger, after disconnecting from heat exchanger, correct?. And am I also correct in saying your drive unit has a raw water pump built inside the drive unit (as in an Alpha Drive)? If that is the case, then you won't get water backwards thru the drive since you'll be trying to force water back thru the pump, which you won't do, except for a little bit of dribble.

If I were doing it, I would pull the drive off and then backflush. You should get a good stream of water then. I would also split the drive sections and check for any pieces of the old impeller stuck in there. Put her back together, put muffs on her and run that hose into a bucket, not the heat exchanger and start her up and run for about 15 seconds. Should get about 6-7 qts of water out of the hose in that 15 seconds. If you do, then you are clear to the heat exchanger and I would be looking at the water flow thru rest of raw water system. Some closed cooling systems use engine coolant to cool the manifolds and raw water to cool the elbows (full system will have 2 hoses going to each manifold) and some use raw water to cool manifolds and elbows (1/2 system will have 1 hose going to manifold). Gotta look at your hose routing to figure out which one you have.

 

[stonyloam]

Re: 1987 mercruiser 165hp 3.7

on the transom, the hose connects to a plastic piece which has a square housing.

Ok that is your water inlet from the hose on the outdive. That hose should go alongside the engine to a voltage regulator which is a box about 4" square bolted to the side of the engine with wires coming and going from it. It has an inlet and outlet where the hose is attached. If it is not there, someone has probably converted to an alternator. Is there a belt driven automotive style alternator on the front of the engine? Anyway that hose goes into the front of the heat exchanger, water flows back and forth through the exchanger and out through the aft hose fitting,then up to the power steering cooler (if you have one) and up to the exhaust elbow,where the water exits the engine. If you can remove the hose from the exhaust, and remove the hose from the transom fitting, backflush by putting a garden hose on the exhaust hose, and see if you have good flow. If you have good flow then your clog is in the hose from the bellhousing, you need to pull the outdrive and backflush or run something through to to clear it out. BTW you have a "full" closed cooling system, where the exhaust manifold is cooled by antifreeze. Good luck.